Integrating Microbial Insecticides and Oils into Sweet Corn IPM in Massachusetts

Final Report for ANE95-026

Project Type: Research and Education
Funds awarded in 1995: $0.00
Projected End Date: 12/31/1997
Matching Non-Federal Funds: $10,598.00
ACE Funds: $30,138.00
Region: Northeast
State: Massachusetts
Project Leader:
Ruth Hazzarad
University of Massachusetts
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Project Information


[Note to online version: The report for this project includes tables that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact Northeast SARE at (802)-656-0471 or]

Fresh market sweet corn is a major vegetable crop in the Northeast. In Massachusetts, it comprises about half of the acreage in vegetables, with 8,000 acres grown. Caterpillar pests of corn, which feed directly on sweet corn ears inside the husk, cause from 10 to 100% unmarketable ears if left uncontrolled. Currently, farmers have no alternatives to restricted-use broad-spectrum insecticides that deplete beneficial insects and have high mammalian toxicity. This project evaluates foliar and direct silk applications of microbial insecticides and vegetable oils as alternative methods which pose less risk to applicators and the environment and which conserve natural enemies. Farmers were involved in the conception and evaluation of these methods through farmer-to-farmer meetings and on-farm trials.

In early season corn, European corn borer (ECB) is the primary insect pest. Commercial Bacillus thuringiensis products were tested in 1994-1996, in 34 trials conducted on 17 farms in Massachusetts. Standard sweet corn IPM scouting methods, thresholds and spray intervals (5-7 days) were used. Bt products gave equal control of European corn borer compared to conventional materials. Higher numbers of beneficial insects were present in Bt-treated plots than conventional plots following insecticide applications. Eighty-two percent of participants were satisfied with the control they achieved and plan to use Bt in their early corn in the future.

Replicated experiments at U. Mass. showed that weekly applications of Bt products were as effective as twice-weekly applications in controlling ECB. The cost per acre of using Bt products is equal to conventional products. The environmental impact as measured by the environmental Impact Quotient (EIQ) is 6.99 for Bt vs. 21.64 for conventional insecticides. An average of 1.0 pt AI/acre of restricted pesticide would be eliminated by adoption of Bt products for early-season ECB control. These results show that Bt products can be integrated into a standard IPM system for ECB control as a direct replacement for conventional insecticides with no extra cost to growers and with positive benefits to the agro-ecosystem.

In late-season corn (harvested in August and September), second-generation European corn borer (ECB) and corn earworm (CEW) cause up to 100% damaged ears. Application of an oil/Bt barrier to the silk at the tip of the ear causes mortality to any caterpillars that enter through the silk channel. Through replicated experiments we determined the timing and rate of application, type of oil, and ratio of Bt to oil to obtain the best control with optimal kernel development. Oil barrier treatments consistently yielded 2-3 times more marketable ears than untreated controls, with results ranging from 65% to 100% undamaged ears compared to 18 % to 87.5% clean in controls. Commercially acceptable levels of control (90-100% undamaged ears) were achieved in experiments where foliar applications of Bt were used in combination with a direct-silk oil treatment. A hand-held oil applicator was designed and built which reduces the labor required for direct treatment of silks. The cost for this late-season biointensive system is $107 to 137 per acre compared to $108 for standard IPM and $172/acre for conventional, non-IPM management. This integrated approach is a promising strategy for late-season corn.

The late-season system was piloted by six growers in 1997 and will be further tested by growers in 1998. This strategy is of greatest interest to organic growers who currently have no method of control for corn earworm, and face significant loss in crop value and sales due to corn earworm damage. If it proves to be reliable and cost-effective it will also be of interest to IPM sweet corn growers with 10-15 acres who are seeking alternative methods.

The results of this project are applicable throughout northeastern and central North America, where fresh market sweet corn has a similar pest complex. Information has been disseminated through presentations at grower conferences, twilight meetings and scientific meetings, and in Extension bulletins, fact sheets and newsletters.

Project Objectives:

1. Evaluate the effectiveness of commercial Bacillus thuringiensis products against European corn borer and fall armyworm in fresh market sweet corn in Massachusetts.

2. Develop an alternative control for corn earworm using an oil and Bacillus thuringiensis barrier applied directly to the silk.

3. Integrate alternative insect controls into current Integrated Pest Management systems used by sweet corn growers in the Northeast.


Click linked name(s) to expand
  • Ruth Hazzard
  • David Holm
  • Steve Mong
  • Brian Schultz


Materials and methods:

The UMass Research Farm is located in South Deerfield, Mass, on river-valley soils close to the Connecticut River. On-farm trials were conducted throughout Massachusetts (in 6 counties) on diversified vegetable farms with variable topography typical of New England. Each farm is managed by a single family or extended family, with total farm size ranging from 20 acres to 150 acres. Corn is grown in 2-15 acre fields bordered by woodlands, other farmers’ fields, or residential homes. Insect pressure was significant at all locations.

Research results and discussion:

Objective 1, Experiment I. On-Farm trials with Bt products, 1994-1996

The purpose of these trials was to determine whether products containing Bt provide control of European corn borer (ECB) and fall armyworm (FAW) as effectively as conventional broad-spectrum insecticides. On-farm trials were conducted from 1994-1996; SARE funds supported the second and third year of trials.

Project description: Seventeen farms participated over the three years, with 10-13 farms each year. Early plantings of corn were split, with one half treated with Bt products and the other half with conventional materials. Some farms compared Bt to unsprayed blocks. The same monitoring methods, action thresholds and timing of applications were used in both treatments, with 1-4 applications per block. Bt products contained B.t. kurstaki; conventional products included methomyl, permethrin, esfenvalerate, and thiodicarb. Scouting was conducted by UMass field technicians. All crop management activities and harvest samples were done by farmers. In 1996, beneficial insect populations were assessed at six farms.

Results: Thirty-four trials were successfully completed. ECB populations exceeded the action threshold in all but two trials. No fall armyworm was present, so the efficacy of treatments against this pest could not be evaluated. The mean ear damage at harvest was equivalent in Bt and conventional treatments (see Table 1). Two categories of beneficial insects (ladybeetles and insidious flower bugs) were consistently higher in Bt plots on the six farms where sampling was done. Higher numbers of dead beneficial insects were found in all conventional plots.

In six trials, corn earworm flights began during silking and the Bt applications were followed by a broad-spectrum insecticide for corn earworm control. There was no difference in the ECB control obtained in these trials compared to those where no CEW flight occurred and only Bt was used. This pest situation is common in mid-season corn. The combination of tassel treatments for ECB with silk treatments for CEW can be readily integrated into existing pest management practices during mid-season. See Pest Management Systems for Sweet Corn, Appendix 2.

Six trials in three years used unsprayed blocks to compare to Bt treated blocks. The average damage levels were 3.4% Bt blocks and 19.9% damage in unsprayed blocks.

Grower evaluations: Of the 17 growers who participated in these trials, 14 (82%) were satisfied with the control they achieved with Bt and plan to use Bt products in the future for ECB control. Three were not completely satisfied and wanted to test Bt further before using it widely on their sweet corn crop. Growers reported that their reasons for choosing Bt over conventional products were applicator safety, easier relations with neighbors, shorter re-entry and preharvest intervals, and conservation of their beneficial insects.

Attachments: For further details, see Using Bacillus thuringiensis (Bt) Products for European Corn Borer Control in Sweet Corn. 1994-1996 On-Farm Trials: Final Report

Objective 1, Experiment II. Replicated trials with Bt products, 1996

The purpose of this experiment was to evaluate several factors in the use of foliar applications of Bt products against European corn borer (ECB).

Project description: Two Bt formulations, Dipel EStm (Abbot Laboratories) and MVPtm (Mycogen Corp.) were evaluated with and without spreader-sticker, and in weekly vs. twice-weekly applications, in field trials using a randomized complete block design at the UMass Research Farm. In one treatment tested, oil was applied to silks (Dipel ES/corn oil, 1:20) in addition to foliar Bt applications. Ears were harvested and rated for damage and presence of pests.

Results: This trial was designed primarily to evaluate control of ECB; however, corn earworm (CEW) was numerous and caused more feeding damage than ECB. All treatments resulted in more clean ears (61-91%) than the control (51%). Although foliar sprays of Bt are generally regarded as ineffective against CEW, in this trial five of six foliar Bt treatments suppressed CEW. The best control (91% clean) was achieved with an oil direct silk application in addition to foliar sprays. The benefit gained by using a spreader-sticker or spraying twice weekly was not significant in most instances. However, one formulation (Dipel ES) resulted in more damage when used weekly without a sticker. In other respects, there were no differences between the two Bt products tested.

Attachment: Foliar Sprays of Bacillus thuringiensis in early corn, 1996. Ruth Hazzard and Mark Mazzola. Arthropod Management Tests: 1997, pp. 122-123.

Objective 2. Develop an alternative control for corn earworm and other late-season pests.

Introduction: Since 1992, we have been investigating oils as an alternative control for corn earworm and other late-season pests of corn. We began this work as a result of an earlier SARE-funded project, New England Farmer to Farmer Information Exchange, which brought together farmers to discuss biointensive methods for sweet corn. One grower was using the oil method successfully on his farm, and others were interested. The method, which was widely used in corn before the introduction of broad-spectrum insecticides, is very simple: small amounts of oil are applied directly to the silk of each corn ear shortly after the corn silk develops. Studies conducted from 1992-1995 demonstrated that either mineral oil and corn oil, mixed with a Bt product and applied once at 0.5 ml/ear, significantly reduces damage from both corn earworm and European corn borer larvae that enter the ear through the silk channel. The oil is applied by hand, by an individual walking down each row. Growers with a total of 10-15 acres of sweet corn would typically be treating a one-quarter to one-acre block of corn at one time.

We have worked closely on this project with the Lemelson National Program for Invention, Innovation and Creativity at Hampshire College. The major barrier to adoption of the oil method is the lack of an efficient applicator tool that will minimize the time required for oil applications. In 1996, with Lemelson funding, we designed and built a hand-held syringe pump oil applicator. Subsequently, the University of Massachusetts and Hampshire College submitted a patent application for this design to the US patent office. Timing trials by researchers and growers indicate that the labor for oil applications to an acre of corn ranges from 6 to 10 hours. Cost estimates for the oil method are based on these figures.

All experiments described below were conducted with four replicates in a randomized complete block design.

Objective 2, Experiment I. Applefield Farm, 1996. The objective of this trial was to determine the effect of different ratios of Bt to oil in the direct-silk oil barrier method.

Project Description: A commercial block of corn was divided into replicated plots with five treatments: Bt (Dipel ES) mixed with corn oil at three ratios (1:20, 1:10 and 1:5), oil alone, and no treatment. The corn was treated on the fourth day after silk initiation.

Results: Untreated ears were heavily infested with corn earworm, with only 18.5% of ears free of damage. ECB and FAW were negligible. Oil alone gave 46.5% clean ears, and the addition of Bt at any ratio significantly improved control (55-65% clean ears). There was no difference in the control achieved by the three oil:Bt ratios.

Objective 2, Experiment II. Applefield Farm, 1996. The objective of this trial was to compare two Bt products and two types of oil for efficacy against the insect complex. Mineral oil has given better control in previous experiments but would not be acceptable on certified organic farms because it is a petroleum product.

Project Description: A commercial sweet corn planting was divided into replicated plots. Two Bt products, Mattchm (Mycogen Corp.) and Xentaritm (Abbott Labs) were applied with either corn oil or mineral oil; three additional treatments with each oil alone or no treatment were used as controls. Xentari, a granular product, was premixed with water but because of a mixing error it was applied an excessively low rates. Applications were made three days after silk initiation.

Results. Corn earworm was the dominant pest. Ear damage was high, with 48% clean ears in untreated plots. There was no significant difference in the control achieved with the two types of oil, whether they were mixed with Bt or used alone. The addition of Xentariâ„¢ to either oil did not give improve control; this is very likely due to the low rates used. The addition of Mattch did significantly improve control, providing 81% clean ears when mixed with corn oil.

Objective 2, Experiment III. Food Bank Farm, 1996. The timing of oil applications relative to pollination of the corn silk affects the length of the filled portion of the ear. Some oil-treated ears have a short, distinct section of unfilled kernels at the tip, which we call a “cone tip�. Untreated ears usually show a gradation of unfilled kernels out to the tip. The timing of application also influences the degree of control, because too late an application will allow insects to enter the ear before the oil is present. The objective of this experiment was to evaluate the effect of the timing of oil application on these factors.

Project Description. A commercial corn planting was subdivided into replicated plots. An oil/Bt mixture (20:1) was applied at 0.5 ml per ear at 2, 4, 6, 8, 10 and 12 days after silk initiation.

Results. Both corn earworm and ECB were present, but infestations were light. Untreated plots were 87.5% clean. The best control (98% clean) was achieved with treatments on day 2 and 4. Subsequent applications provided levels of control that were not significantly different from untreated ears. However, there was a significant trend over all treatments toward better control with earlier applications. Day 2 treatments had a much higher proportion of “cone� tips (26%) compared to day 4 (8%). All later dates had 1% or less, the same percentage as the untreated control.

Objective 2 and 3, Experiment IV. UMass Research Farm, 1996. The major objective of this experiment was to determine whether the rate of the oil/BT mixture applied to silk would effect the degree of tip fill and would change its efficacy against late-season pests.

One limitation of oil applied to the silks is that it does not control insects that burrow through the side of the husk. Many ECB and FAW larvae enter ears through the side, after moving down from the tassel where they fed as young larvae. This “side damage� is a major reason that oil treatment experiments have not consistently achieved the 90-95% control that is needed in most markets. In this experiment, we tested an integrated system in which two foliar applications of a BT product were made at the tassel stage to reduce the number of ECB that would move into ears through the side of the husk.

Project Description. In replicated plots of late sweet corn, a 1:20 mix of Dipel ES: corn oil was applied four days after silk initiation at the following rates: 0.3 ml, 0.6 ml, 0.9 ml or 1.2 ml per ear. An additional treatment used 0.6 ml per ear but was preceded by two applications of MVP II (Mycogen Corp.) five days apart, at the pretassel and tassel stage. At harvest, ears were measured for total length and the length of the filled portion of the ear in addition to damage and insect ratings.

Results: ECB was the major cause of ear damage in this experiment, although corn earworm was also present. There was no fall armyworm. Only 24% of the corn in untreated plots was free of insect damage, and both side and tip damage were present. Oil treatments yielded 64-77% damage-free corn, a three-fold improvement. The addition of two foliar Bt sprays gave 100% clean ears, a significant improvement over all the oil-alone treatments, and certainly a level of control that is acceptable in all markets.

There was no difference in the level of control or the length and proportion of filled kernels with different oil rates. Oil applications resulted in a mean reduction in total ear length of 7% (1.4 cm), a 9% reduction in the length of the filled kernels (1.5 cm.), and a higher proportion of “cone� tips, compared to untreated ears. However, the lowest oil rate (0.3 ml/ear) resulted in a significantly lower percentage of “cone� tips (61% compared to 13% in untreated and 80-85% in other oil treatments).

Objective 3, Experiment I. UMass Research Farm, 1997.

The objective of this experiment was to evaluate the efficacy of elements of the biointensive system for late-season sweet corn.

Project Description: Two foliar applications of Bt at the tassel stage and application of the oil barrier directly to silks were used singly or in combination in late corn that was harvested in mid-September.

Results: Both CEW and ECB caused feeding damage, but CEW larvae were most numerous. Foliar Bt sprays by themselves were ineffective in this study. This may be due to the fact that ECB infestations were low during tasseling and occurred primarily during ear development, with small larvae entering directly through the silk channel. The control achieved by oil treatments was 32.9% better than the control. There was no statistical difference between the control achieved with oil alone and that gained with oil plus Bt sprays.

Attachments: See 1997 Annual Report of the Vegetable and Small Fruit Integrated Crop Management Program, p.30-31, for further details.

Participation Summary


Educational approach:


1. On-Farm Trials of Bacillus thuringiensis (Bt) Products for European Corn Borer Control: Year Two Report, a two-page fact sheet on results of 1994 and 1995 trials, was distributed to 240 subscribers to the UMass Extension newsletter, and at grower meetings (150 growers). It was also published as an article in the New England Grower.

2. Foliar Sprays of Bacillus thuringiensis in Early Corn, 1996. By Ruth V. Hazzard and Mark Mazzola, in Arthropod Management Tests: 1997, pp.122-123. Results of Objective 1, Experiment II, Replicated trials with Bt products, 1996.

3. 1996 Annual Report, Vegetable and Small Fruit Integrated Crop and Pest Management Program. This report was submitted to the IPM Steering Committee at the University of Massachusetts, distributed to the Advisory Committee of the Vegetable and Small Fruit Program (including 14 growers), and made available through the UMass Bulletin Center. Research results from this project are reported in the sweet corn section (pp. 21-29).

4. Biointensive insect management in sweet corn, a four page fact sheet, was written in 1997 and distributed to attendees at NOFA workshops, twilight meetings, and the Northeast SARE conference.

5. A 7-page Extension bulletin, Using Bacillus thuringiensis (Bt) Products for European Corn Borer Control in Sweet Corn. 1994-1996 On-Farm Trials: Final Report, was published by UMass Extension, Publication #C-220, 1997. This report was sent to all participating growers in the BT trials and is available at the UMass Bulletin Center (413-545-2717).

On-Farm Trials of Bacillus thuringiensis (Bt) Products for European Corn Borer Control: 1994-1996. Final Report. Published in the Grower, with circulation throughout New England. Part I, April 1997, pp 1-4. Part II, may 1997, pp2-4.

6. Vegetable Pest Messages, summer 1997. Weekly pest alerts included recommendations on using Bt products for ECB control. Sent to 250 subscribers.

7. 1997 Annual Report, Vegetable and Small Fruit Integrated Crop and Pest Management Program. See 1996 Annual Report for audiences who will receive this report. Includes 1997 research results from this project, pp. 30-31.

Educational programs:

1. Twilight meeting, August 8, 1996, at Applefield Farm in Stow Mass. Demonstration of oil applicators and discussion of oil and Bt applications with 40 growers at one of the cooperating farms.

2. Twilight meeting, September 11,1996, Morning Glory Farm, Martha’s Vineyard. This is a location with extremely high corn earworm pressure and several diversified farms that are seeking alternative methods for corn earworm control. The oil applicator method was discussed with 20 growers. One grower subsequently participated in trials in 1997.

3. Workshops on biointensive insect management in sweet corn were conducted at the winter conferences of Vermont NOFA (February 15,1997) and Massachusetts NOFA (January 18, 1997). Growers Steve Mong and Tom Harlow shared the presentations in MA and VT, respectively.

4. Presentation entitled, “Use of Microbials and Oil for Control of European corn borer and Corn earworm� was made at the Eastern Branch ESA meeting, Burlington VT, February 25, 1997. This was part of a symposium on Development of Biointensive Sweet Corn IPM, organized and moderated by Ruth Hazzard.

5. Twilight meetings , July 16, 1997 at Food Bank Farm, Hadley, MA and August 13, 1997 at Hutchins Farm, Concord, MA. Biointensive strategies for late-season insect management were demonstrated and discussed.

7. Planned: A presentation on alternative methods for insect control in sweet corn will be made at the New England Vegetable and Berry Conference, Dec 17, 1997

8. Planned: A workshop on managing sweet corn will be presented at the NOFA-Rhode Island annual meeting on March 7, 1998.

Project Outcomes

Impacts of Results/Outcomes

Farm Profits and Production Levels. For growers currently using registered broad-spectrum insecticides, Bt foliar sprays provide an alternative that is no more costly and can be readily integrated into current practice. Its benefits are greater applicator and worker safety, better relations with neighbors, and conservation of natural enemies. Since diversified vegetable production increasingly takes place on the urban fringe, use of safer materials will be critical to the survival of these farms in the future. The late-season system is also an equal or slightly more expensive alternative with comparable benefits. For organic sweet corn growers who currently see retail sales decline and are prohibited from wholesale markets, a viable organic method will expand sales, production and profitability. As one organic farmer put it, ‘instead of having to throw out [Ed. note: text was missing in original report.]

Pesticide reduction and environmental impact. The ultimate goal of using Bt’s and oils in place of conventional broad-spectrum insecticides is to lessen the environmental impact on agro-ecosystems. We have assessed that impact by two measures: the EIQ and quantity of active ingredient of restricted pesticide applied per acre.

The attached table, Pest Management Systems for Sweet Corn [See original report] shows in detail the calculation of the impact of biointensive methods on the total active ingredient (AI)of pesticide applied per acre and the total field EIQ. A summary of the pesticide reductions that could be achieved over the course of the season is as follows:

1. EIQ. A scale devised by Kovach, et al. (1992) quantifies the environmental impact of different pesticides through a numerical formulation known as the Environmental Impact Quotient, or EIQ. The EIQ for a specific pesticide is determined by a formula which includes toxicity to humans, water solubility, half-life, and toxicity to fish, birds, bees, and beneficial insects. A higher EIQ indicates a greater negative impact on the environment. This scale has been criticized as weighing some factors inappropriately; however, it is the only comprehensive environmental measure currently available. By providing an index of the relative impact of a particular pesticide on the environment, it allows comparison of different management programs. The actual rate used and the number of applications is multiplied by the EIQ of each material to give a Total Field EIQ.

2. The quantity of active ingredient of toxic materials applied per acre. This is expressed in pints per acre (Table 4) or pounds per acre (Table 5). The pesticide reduction potential for the methods tested here is high by either measure. Actual reduction levels will depend upon the extent of adoption. Bt products are general-use materials with low toxicity, and they carry the signal word “caution� on the label. Vegetable oil is exempted from registration requirements under the Section 25b provision of FIFRA. Most broad-spectrum insecticides used in sweet corn are restricted-use.

The following chart provides information on current materials that could be replaced by microbials and oils. Calculations are based upon the average number of applications per season per acre used by IPM cooperators in Massachusetts, 3.5 applications per acre. Non-IPM growers use more. Massachusetts has over 8,000 acres of sweet corn; New England has at least 20,000. Figures are given for total active ingredient of a given material that would be applied to 1,000 acres if only that material was used. [See original report for chart.]

New Hypotheses

1. The integration of two foliar sprays of Bt with oil applications will give consistent, high levels of control of both corn earworm and European corn borer throughout the season and provides a viable and practical system for pest management in mid and late-season sweet corn.

2. Use of biointensive methods in corn will result in higher populations of beneficial insects in corn and other crops on diversified vegetable farms with increased suppression of other insect pests such as aphids.

Economic Analysis

We have used partial budget analysis to assess the economic impact of substituting these alternative practices for conventional or standard IPM practices.

1. Use of BT for European corn borer control. Standard IPM monitoring methods and thresholds are used and the number of applications is the same with biointensive vs. conventional practice. The only difference in cost is the material itself, which varies somewhat with the material chosen and the supplier. Table 3 compares the costs per application for Bt vs. conventional foliar sprays. This assumes use of Dipel ES for Bt applications and Lannate for conventional applications. There is no difference in cost for the two methods.

2. Late season biointensive system for European corn borer and corn earworm control. In Table 3, partial budget analysis is used to compare three late-season systems:
1. A biointensive system in which two foliar applications of Bt during tassel are followed by one oil/Bt application to the silk of each ear. Because we have observed a range of 6-10 hors per acre to make an oil application, we are reporting the corresponding range of costs.
2. A standard IPM spray regime for late-season corn, in which 5 applications of a broad-spectrum material are made to each block of corn. This figure is based on the mean for IPM cooperating growers in Massachusetts.
3.A “conventional� or non-IPM spray regime for late-season corn, in which 8 applications of a broad-spectrum material are made to each block of corn. This figure is based on pre-IPM practices in Massachusetts.

Summary: The relative cost for late-season systems depends on the number of insecticide applications used in a standard IPM or conventional system, and the number of hours required to make the oil application. The biointensive system ranges from $1.02 less to $28.98 more than the standard IPM system, and from $65.58 to $35.58 less than the conventional non-IPM system.

3. Other costs. There are other characteristics of the two systems that are difficult to quantify but would affect the real cost to the grower in terms of time and management choices. These include:

1. Safety. The benefit of great safety for the applicator, when Bt products are used.
2. Beneficial insects. Additional pest suppression is provided by natural enemies which are conserved when biointensive systems are used. These include predators and parasites of European corn borer eggs and corn leaf aphids. Outbreaks of aphids are common in sweet corn during July and August. Methomyl (Lannate) is widely used to control aphids, but further depletes natural enemies.
3. Effects of weather. Weather conditions must be considered at the time of each foliar insecticide application. Minimal air movement is critical for good coverage and minimizing drift. Lack of rainfall before, during and for a day or two after the application is also important. With the oil direct silk method, the application is made once and is not affected by windy or wet conditions.
4. Number of applications. The IPM/conventional system requires 5-8 applications, each of which must consider the weather conditions. With the oil method, there is a single application. This affects the time and decision-making investment required by the grower.
5. Labor. Oil methods have significantly different labor requirements. Pesticide applications are typically made by the farmer or a long-term employee, who must be a certified pesticide applicator. The oil application requires more hours, but it can be done by hired summer employees at a lower wage rate. Since the farmer’s time is at a premium during the busy season, shifting the task to other workers could be advantageous.
6. Hand labor. Another “cost� is the “paradigm shift� required by the oil method. The concept of making an application to every corn ear by hand is a barrier for most sweet corn growers. Despite the outcome of partial budget analysis, adopting a method that requires more hand labor goes against a trend and a mindset that supports mechanization of production.
7. Ownership cost of equipment. For small growers, investment in tractor-mounted spray equipment can be prohibitive. The oil method provides substantial pest control with an investment under $150 for a hand-held applicator.
8. Access to organic markets. Currently, organic sweet corn producers in New England cannot sell to wholesale organic markets throughout the season because their mid and late season corn is infested with unacceptable levels earworm. This method would give them access to markets that demand clean corn.
9. Retention of customers. Organic sweet corn producers who sell retail in direct markets report that customers leave and sales drop after corn earworm arrives and corn becomes infested. Because corn is an “anchor� crop in farm stands, retaining sweet corn customers means not only getting a return on the sweet corn crop but retaining sales in other crops as well.
10. Posting of fields. Fields treated with restricted pesticides must be posted with warning signs along public highways; fields managed with biointensive methods would not.
11. Potential for drift. Growers using restricted materials must be extremely careful to avoid drift onto neighbor’s fields and homes. This is not as serious a concern with Bt’s and no concern with oil applications.
12. Re-entry interval. Workers may not enter fields treated with restricted materials for 24-48 hours. This limits harvest and other field work. Biointensive methods have 0-4 hour re-entry.

Farmer Adoption

Changes in practice

This project has not yet conducted a formal survey to measure adoption of these methods among sweet corn growers. Dissemination of information to all sweet corn growers is still in progress. A formal assessment of adoption should be conducted after educational programs are completed.

Requests for information about the oil method have come from farmers in Vermont, Maine, Massachusetts, New Hampshire, Rhode Island, and Connecticut, Pennsylvania, and Washington State. Six growers participated in testing the oil method and applicator in1997 and are interested in repeating this in 1998.

Operational Recommendations

1. Replace broad-spectrum insecticides with Bt products for control of European corn borer in sweet corn, following IPM methods for monitoring and decision-making. For more details, see Using Bacillus thuringiensis (Bt) Products for European Corn Borer Control in Sweet Corn. 1994-1996 On-Farm Trials: Final Report, UMass Extension Publication #C-220, 1997.

2. Growers who want an alternative to broad-spectrum materials for corn earworm and European corn borer control can achieve effective control using Bt foliar applications during tassel and a single direct-silk oil/Bt application at the beginning of ear development. Details can be found in the fact sheet, Biointensive insect management in sweet corn.

Farmer Evaluations

Eighty-two percent of growers who participated in the 1994-96 on-farm Bt trials were satisfied with the control achieved by Bt, and planned to use it for ECB control in 1997 (see Using Bacillus thuringiensis (Bt) Products for European Corn Borer Control in Sweet Corn. 1994-1996 On-Farm Trials: Final Report, p 6. Growers who tested the oil applicator and oil method in 1997 reported positively on the efficiency and ease of the applicator itself and on the improvement in control. All are interested in repeating these trials.

Producer Involvement

Number of growers in attendance at workshops/conferences : 50; at field days: 120
Number of growers receiving educational materials: 300

Areas needing additional study

1. Biointensive methods for corn earworm control that are viable and effective on large scale sweet corn farms (>100 acres).

2. Integration of biological control agents such as Trichogramma ostriniae into biointensive IPM strategies.

3. Impact of adopting biointensive methods on whole-farm viability at the urban fringe.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.